Apparatus for drying tobacco



Dec. 12 1967 A. H. WRIGHT 3,357,436

APPARATUS FOR DRYING TOBACCO Filed Aug. 26, 1964 Y\ m I m Q N I 0 I l I l I Q I I Q l l I I I Q I \J I I I I b 3 I Q N i w N m I I I v I I I Lb m I N N I J l 1 l N\ I r S Q 2 I Q Er R Q 3 Q Q Q N INVENTOR.

AZL'XIM/DER HERBERT WRIGHT ATTORNEYS United States Patent ice 3,357,436 APPARATUS FOR DRYENG TOBACCO Alexander Herbert Wright, London, Middlesex, England, assignor to Brown & Williamson Tobacco Corporation, Louisville, Ky., a corporation of Delaware Filed Aug. 26, 1964, Ser. No. 393,431 18 Claims. (Cl. 131-135) ABSTRACT OF THE DISCLOSURE Drawing of tobacco by a substantially closed system in which air is circulated and heated. The tobacco is introduced into the heated air and then conveyed by the air stream through at least one heating chamber to effect the desired drawing. Thereafter, the tobacco is separated from the air stream and subsequently cooled. A portion of the moist air is then removed and a corresponding amount of fresh air introduced into the system. The moisture content and the temperature of the air in the system are independently regulated to assure that the tobacco discharged from the system is maintained at a substantially constant moisture content.

This application is a continuation-in-part of application Ser. No. 233,233, filed Oct. 26, 1962, now abandoned.

This invention concerns improvements relating to the treatment of tobacco with a gaseous medium for the pur pose of drying the same, that is, for the removal of moisture from the tobacco or providing it with a uniform predetermined moisture content. Generally, the gaseous medium will be hot air, although other suitable media may be employed. The term air used hereinafter is to be understood to include such other media. Furthermore, the invention has particular application to the treatment of cut and green strip tobacco as well as other forms of tobacco including destemmed or whole leaf tobacco.

A method of drying tobacco by means of hot air has been described in the specification of United States patent application of Anderson et al., No. 828,619, filed July 21, 1959, now abandoned. It has been found that tobacco which has been dried by that method, when compared with tobacco dried by other known methods, may have lesser filling power. That is, cigarettes made from the tobacco may be less firm or, alernatively, a greater quantity of tobacco may have to be used to obtain the same firmness. The present invention is in part concerned with modifications to the aforesaid method whereby the filling power and quality of the to bacco can be improved. The invention has the further advantage that the moisture content of the tobacco can be rendered even more uniform and, consequently, the quality of the cigarettes more uniform.

A further object is to provide an air drying system for tobacco which may readily be designed to turn corners, extend from room to room or floor to floor, or assume a straight line layout.

Another object is to provide savings in upkeep, maintenance and cleaning with a system incorporating the teachings of this invention compared with other known or commonly employed equipment for conditioning tobacco to have a certain moisture content such as the known apron dryer for 'redrying green strip tobacco.

According to the invention, for improving the filling power of tobacco, drying is effected, preferably in accordance with the aforesaid method, by using as a drying or drying and conveying medium hot air containing a high proportion of water vapor. To ensure a high proportion of water vapor, there should be present not less than 1 part, by weight, of moisture to parts of dry air. Generally, however, there should not be less than 1 /2 parts of mois- Patented Dec. 12, 1967 ture to 10 parts of dry air. For example, by the use of air containing 1 part of moisture to 5 parts of dry air, a greater filling power than is obtained by well-known methods of drying can be achieved. Although an increase in the moisture content of the air results in a reduction in the quantity of moisture extracted from the tobacco in the drying apparatus, it increases the quantity of heat carried by the tobacco at its dis-charge from the apparatus. This increased heat results in an increase in the quantity of moisture extracted in subsequent cooling and, consequently, the total quantity of moisture extracted is not substantially reduced by the increase in the moisture content in the air.

It would be possible to provide air having the required moisture content by injecting into the air at its entry to the dryer either steam, Water in the form of a fine spray or a combination thereof. The quantity of steam, or of water to be evaporated in the air, would then considerably exceed the quantity of moisture to be extracted from the tobacco. Consequently, the heat consumption of the apparatus would be excessive. Furthermore, uniformity in the proportion of water vapor to air would not be readily obtainable by this method.

According to a preferred manner of carrying the invention into effect, the water vapor content of the air is arranged to be provided, either wholly or in part, by moisture evaporated from the tobacco. This can be achieved by causing air to circulate continuously in a substantially closed system. It will be understood that if the whole of the air were allowed to recirculate, its content of water vapor would increase until the air was no longer capable of taking up moisture from the tobacco. Accordingly, a large proportion, say not less than one-half of the air flow, is caused to be recirculated. In this manner of performing the invention, the water-vapor content of the air is regulated by causing a small proportion as, for example, about one-twentieth, of the air flow to be continuously discharged from the system and introducing an equivalent quantity of fresh air. The greater part of the excess water vapor will then be carried off by the discharged air and the remainder will be condensed by the cooling effect of the fresh air and can be drained away.

The quantity of fresh air introduced may be so controlled automatically as to maintain a constant air temperature in the region of condensation, whereby the proportion of water vapor to air can be regulated and maintained constant. The quantity of fresh air introduced may also control the quantity of air discharged from the system. If, there should be excessive loss of moisture from the system, due for example to leakage of air at the points of entry of the tobacco to or discharge from the system, it may be necessary to add some steam and/ or water to the circulating air. The quantity of steam or water then required will, however, be very much less than with the method referred to above.

In the apparatus described in the aforesaid specification, provision was made for recirculating a proportion of the air. However, in that case, it was not possible to regulate both the temperature and the moisture content of the air independently. Furthermore, only a small proportion of the air could be recirculated, as otherwise the intake of hot air would be insutficient. In the preferred manner of carrying out the present invention, the temperature of the air at the point where the tobacco is discharged may be regulated by causing a variable proportion of the circulating air to pass through the heating apparatus and the remainder of such air to by-pass the said apparatus and to be recirculated without reheating.

Water in the form of droplets may be removed from the air by means of a chamber containing a series of baffle plates or any other known means. Impingement of the air on the wetted plates then also removes from the air suspended particles of fine tobacco dust which would otherwise form harmful deposits in the heating apparatus. Naturally, other known means for removing moisture and dust can be employed.

Drying apparatus in accordance with the present invention may, accordingly, include preferably in combination with apparatus such as is described in. the aforesaid specification, means for recirculating a large proportion of the hot air, means for replacing a proportion of such air by fresh air, means for maintaining a constant proportion of water vapor to air, means for removing from the air water droplets and fine tobacco dust, and means for regulating the temperature of the air independently of its water-vapor content.

Ways of carrying the invention into effect will now be more fully described by way of an example and with reference to the accompanying diagrammatic drawing.

In the system shown in the drawing, air is delivered by a fan 1 to a duct 2, the quantity of air being regulated by a manually operated damper 3. Tobacco is delivered into the duct 2 by an automatic feeder 4 through an air lock comprising a rotary valve 5 and is conveyed by the air flow through one or more drying chambers 6.

These chambers may be of the form described in the aforesaid specification No. 828,619. In each chamber 6, the tobacco is then conveyed upwardly, the velocity of the air being substantially lower than in the ducts of the system. The chamber is so proportioned in relation to the velocity of air flow that the air flow in the chamber is insufficient to overcome the force of gravity on denser portions of the tobacco, so that such denser portions will lose their initial upward velocity before reaching the top of the chamber and will sink back in the outer part of the chamber and execute a circulatory motion in the chamber until their density has become less. These denser portions of tobacco may be the result of wetness of the tobacco or physical matting.

The tobacco-laden air flows from the last chamber 6 into a separator 7 of known type in which the tobacco is separated from the air and is discharged through an air lock comprising a rotary valve 8 or other known means of discharge. The tobacco is then carried by a conveyor belt 9 to a rotary cooling apparatus 10 of known type.

The air passes from the separator 7 through a duct 11 to a cyclone 12 or other suitable means, in which dust is removed, and thence through a duct 13 provided with a flow meter 13a. A branch duct 14 permits a small proportion of the air fiow to be discharged from the system. The remaining air, which is to be recirculated, passes through a venturi throat or injector 15, thereby creating a local reduction of static air pressure and enabling fresh air to be drawn into the system through a branch duct 16, provided with a flow meter 160, under the control of a damper 17. Of course, other means for introducing air may be employed. A further duct 18 conveys the air from the throat to a chamber 19 in which it impinges on a series of shaped bafile plates on which are deposited any water droplets and any fine tobacco dust carried by the air. Matter deposited on the baffie plates collects at the bottom of the chamber 19 and is discharged through a water seal and separator 19a. The water-vapor content of the air may be increased by the introduction of steam and/or water through a jet 20 either at the point indicated in the drawing or at a point in the duct 13 between the branches 14 and 16. In some cases, the latter location may be preferred for the introduction of water, as water will be more readily evaporated at the higher temperature obtaining in this region and the subsequent cooling by the admission of fresh air at 16 will ensure that the air is saturated before it enters the separating chamber 19.

A temperature-sensing element 21 disposed in the air stream immediately beyond the chamber 19 is connected by a known temperature-responsive controller 21a to the damper 17, whereby the inflow of fresh air can be regulated to maintain a constant air temperature at the element 21. This admission of fresh air tends to increase the static pressure throughout the system and the increase ofpressure at the branch duct 14 will increase the quantity of air discharged at that point. The flows of air into and out of the system are thus maintained in equilibrium.

Air flows from the chamber 19 to a diverting valve 22 which divides the air stream in variable proportions between a heater 23 and a by-pass duct 24. Preferably, steam or hot water is used in the heater 23 for the purposes of heating the air. In this connection, other suitable means for heating air may be employed. A damper 25 in the duct 24 is permanently adjusted to balance the air resistance of the heater 23, so that the total air flow is substantially unaffected by movements of the valve 22.

The flows through the heater 23 and by-pass 24 are recombined and delivered to the inlet of the fan 1, the temperature of the re-combined air being dependent on the relative proportions of the two said fiows. A temperature-sensing element 26 in the duct 11 is connected by a known temperature-responsive controller 26a to the diverting valve 22 for the purpose of regulating the setting of the said valve, whereby a constant air temperature can be maintained at the element 26.

Inasmuch as the amount of moisture removed from a particular tobacco, types of tobacco, blends of tobacco and form thereof will vary, the operating parameters of the treatment system of this invention will vary, accordingly, in producing a uniform and constant moisture content of tobacco discharged from the system. Two important factors which control the operation of the system are:

(a) The hold time of the tobacco within the system,

and

(b) Ratio of volume of air flow to weight of tobacco being discharged.

The quantity of heat required for drying the tobacco will be dependent upon the rate at which the tobacco is fed through the system and upon its initial moisture content. An increase in either the said rate or content will tend to produce a reduction of air temperature at the sensing element 26, so that, with the method of control described above, the heat input will be increased. Similarly, a reduction in feed rate or moisture content will produce a reduction in the heat input. Accordingly, the heat input will be so proportioned, depending upon the conditions, that the final moisture content of the tobacco will be maintained constant.

With an alternative method of control, the heat input is made constant, either by using a fixed setting of the diverting valve 22 or by omitting this valve and the bypass 24, and the temperature sensing element 26 is arranged so to regulate the output of the feeder 4 that a constant air temperature at the said element is maintained. This method of control may be preferred with sources of heat, other than steam or hot water, whose heating effect is not controllable by variation of the air flow through the heater and may not be susceptible to rapid control by other means.

If desired,.a second fan may be included in the duct 11 and 13 between the tobacco separator 7 and the branch 14. It is then possible to arrange that the air pressure in the duct 2 at the point (5) of tobacco entry is nearer to atmospheric pressure, so that a venturi can be used, in place of the rotary air-lock valve 5, for the introduction of the tobacco, as suggested in the above-mentioned specification, without the air velocity in that venturi being excessive. In place of the rotary air-lock valve 8, use may be made of a substantially vertical pipe whose open lower end is a short distance above the belt 9. The speed of the belt is then so controlled that there is at all times a sufficient depth of tobacco in the pope to prevent the passage of air between the separator 7 and atmosphere.

In place of the venturi device 15, use may be made of either a damper or other restriction so located in the duct 13 between the branches 14 and 16- that the pressure at the outlet 14 is above and that at the inlet 16 below atmospheric pressure, or of a small auxiliary fan by which the air is introduced through the branch 16 under pressure.

It has been found that cut tobacco treated in accordance with this invention may, according to the particular requirements, possess a moisture content when discharged by the separator 7 of between 9 to 23 percent. An optimum percentage has domestically been found to reside in the neighborhood of 13%.

With respect to green tobacco, the attainment and maintenance of uniform moisture content is of the utmost importance. As will be appreciated by those skilled in the art, green tobacco is usually stored in hogsheads for generally two years. Experience has proven that, with prior art equipment, the moisture content of the stored green tobacco was not uniform but, to the contrary, was somewhat spotty causing wet locations or concentrations of moisture of suificient magnitude to cause molding of the tobacco. In accordance with the present invention, green tobacco is treated such that it will have a moisture content of between 9 to 18% when discharged by the separator 7 depending upon the particular requirements. For storage purposes, about 11% would represent the lower limit, an optimum value being in the neighborhood of about 12.5%. For certain overseas markets, the duty requirements and Obligations would dictate that the moisture content be held at a value slightly above Tobacco ordinarily introduced into the system of this invention will vary in moisture content. The moisture content of cut tobacco will, accordingly, spread over the outside limits of roughly 16 to 35 percent, the lower limit representing that at which Turkish tobacco is cut whereas the upper limit representing the value at which tobacco in South America is generally cut. In this connection, the lower limit for the Latin American market may even be reduced to a value of 13%. The optimum moisture content for domestic purposes will generally be between 18 and percent. The lower limit, in most instances, being somewhat higher and roughly at 21%.

With respect to green tobacco, the moisture content of the tobacco introduced into the system will generally range between 16 and 25 percent again depending upon the particular conditions and requirements. The usual limits experienced in actual practice for domestic purposes being between 18 and 25 percent, the usual value being at 20%.

In handling both out and green tobaccos with the system of this invention, the ratio of volume of air flow to weight of tobacco being handled will range from 0.5 to 5 cubic feet per minute per pounds of tobacco per hour. Below the lower specified limit, there will be a tendency to lose conveyor velocity whereas, above the upper limit, operating efficiency will be at an impractical level in that choking will be experienced. In handling these tobaccos, the temperature of the inlet air passing through duct tubes will range between 150 and 600 F. The tobacco itself entering this duct from the valve 5 will range between room temperature and 200 F. The temperature of the air emanating from the last chamber 6 will range between 130 F. to a value less than 200 F. With respect to all tobaccos capable of being handled by this invention, about 80% of the air is recirculated. Therefore, about 20% makeup air is generally required. A minimum bleed-off will be in the neighborhood of 5% and, theoretically, there could be a 100% bleed-off but economically this would not be done because of the dissipation of heat for no useful purpose and the requirement that the makeup air be heated to a certain temperature. As stated in the above, bleeding-off of air is desirable for purposes of lowering the percentage moisture of the air.

In order to maintain the desired operating conditions, the temperature at 21 is maintained relatively constant and, generally, will fall between 140 and 160 F. for

the tobaccos generally handled by the system of this invention. It should be understood that this represents the optimum range and temperatures could exceed this range depending upon the particular conditions and requirements and could very well fall between room temperatures and 600 F.

As a specific example of the treatment of cut tobacco by this invention, apparatus was constructed in accordance with this teaching and possessed a nominal capacity of 2500 lbs. of tobacco per hour. In this example, the total fluid flow measured at 13a amounted to 5,400 lbs. per hour of air and 1,150 lbs. per hour of water vapor. To maintain this proportion of air to water vapor, the temperature at point 21 was automatically held constant at a value of about F. The quantity of air entering the system at 16 and discharged at 14 was automatically adjusted to maintain the aforesaid temperature and usually amounted to between 5% and 10% of the total air flow.

The temperature of the air at the point 26 was controlled at a constant value of 175 F. to produce tobacco containing 13 /2 moisture from the cooling means. The temperature of the air at point 2 was automatically varied in accordance with the quantity of moisture to be extracted from the tobacco and usually was within the limits of 200 and 300 F. The moisture content of the tobacco entering the apparatus at 5 varied between 17% and 19% without measurably altering the moisture content at the cooler. It has also been found that the rate of tobacco flow can be varied between 750 and 3,000 lbs. per hour with periodic control adjustments without significant effect on the final moisture content.

The following values represent a typical treatment run for drying out tobacco.

Total air flow s.c.f.m 1,200 Mean tobacco flow (dry weight) lbs. per hour 2,050 Mean moisture content of tobacco before drying percent 17.73 Standard deviation of moisture content before drying do 0.83 Mean moisture content of tobacco after drying and cooling do 13.57 Standard deviation do 0.18 Air temperature at 26 F 175 Air temperature at 21 F 150 Air temperature at 2 F 230-250 Moisture content of air at 21 grains per 1b 1475 Moisture content of air at 26 do 1,560 Relative humidity of air at 26 percent 57.5

Tobacco from the same batch dried in conventional apparatus had a standard deviation of moisture content of 0.62%. The filling power of this tobacco was 2.3% lower than that yielded by the improved method.

A larger capacity system incorporating the teachings of this invention has been successfully employed and was designed for production rates in the order of 12,000, 12,500 and higher pounds of tobacco per hour. In this exemplary embodiment and assuming a production rate of about 12,000 lbs. of tobacco per hour, a total air flow of 17,500 c.f.m. was employed. The air to tobacco ratio was, under these circumstances, 1.33 c.f.m. per pound of tobacco per hour. The temperature at 21 was maintained at substantially F. while the temperature at the point 26 was controlled at a substantially constant value of 175 F. In this instance, the moisture of the tobacco entering the system through the valve 5 was 24.3% at 200 F. The moisture content of the tobacco discharged onto the conveyor 9 was 13.6% at F.

In another run of this higher capacity unit, a mean of 11,500 lbs. per hour of tobacco was introduced. Approximately, 12,100 c.f.rn. of return air was utilized together with 4,670 c.f.m. of makeup air making a total of 16,770 c.f.m. The percentage makeup air in this instance was 28%. The temperature of the air at 26 was 182.5 whereas the temperature at 21 was 160. The temperature in the line 2 at the point of introduction of the tobacco was 210. The mean moisture content of the tobacco before drying by the system was approximately 23% with a standard deviation of about j- 1%. The mean moisture content of the tobacco after drying and subsequent cooling was about 13% with a standard deviation of i.25%. It should be understood that the air temperatures given represent the approximate mean. For example, the temperature at 26 will range between 170 F. to 185 F., the air temperature at 21 will range between slightly below 150 F. to slightly above 160 F. whereas the air temperature in the conduit 2 at the point where the tobacco is introduced will range between 225 to 335 F. The moisture content of the airin this duct at the point of introduction of the tobacco will be roughly 900 grains per pound while the moisture content of the air in the duct 11 after removal of the tobacco will be roughly 1100 grains per pound. Of course, there will be deviation of about 1% but these figures represent the mean. In addition, the relative humidity of the air at 26 will be 38% to 40%.

In connection with the treatment of green tobacco, a further large capacity system incorporating the teachings of this invention was designed and employed. The, total amount of air passing through the system was roughly about 14,800 c.f.m. A production rate of 12,000 lbs. per hour was realized with an air to tobacco ratio of 1.23 c.f.m. per pounds of tobacco per hour. The control temperature of the air in line 11 after discharge of the tobacco was about 184 F. whereas the control temperature 21 was about 175 F. The moisture content of the tobacco introduced into the system was 21% at 90 F. while the moisture content of tobacco out of the system was 14% at 140 F. With respect to the total air passing through the system, 4.200 represents the makeup air which is roughly 28% of the total. In this instance, it was determined that ,the air traveling in line 11 was traveling at the rate of 4,000feet per minute whereas the air in line 18 was traveling at a rate of about 5,600 feet per minute. In this particular application, five chambers 6 were used each having a diameter of approximately 50 inches, with progressively increasing heights of their respective cylindrical portions, notably, 5 feet, 6 feet 3 inches, 7 feet 6 inches, 8 feet 9 inches, and 10 feet. Under the circumstances, it is believed that adequate criteria, and parameters have been set forth herein to enable one skilled in the art to practice the invention and design a treatment system with rated parts without undue experimentation and unnecessary trial and error.

Thus, the several aforenoted objects and advantages are most eifectively attained. Although several somewhat preferred embodiments of this invention have been disclosed and described in detail herein, it should be-understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.

I claim:

1. Apparatus for humidifying air and drying tobacco comprising means for circulating the said air in a substantially closed system, means for heating the air in the system, means for introducing tobacco at one end of the system and in the path of the heated air, means in advance of said tobacco introduction station for moisturizing the air so that the air initially contacting the tobacco contains a predetermined amount of moisture, chamber means in the system at a point beyond the tobacco introduction station and in which the tobacco is conveyed upwardly by the hot moisturized air, the air flow in the chamber means being insufficient to overcome the force of gravity on denser portions of the tobacco so that such denser portions will lose their initial upward velocity before reaching the top of the chamber and will sink back in the outer part of the chamber and execute a circulatory motion in the chamber until the density of such portions has decreased to the desired degree, means for separating the tobacco from the conveying air, means for discharging an'amount of moisture-ladened air from the system, means for introducing the equivalent amount of fresh air at a lower moisture content into the system, and temperature-sensing means for sensing the temperature of the air following the discharge of the tobacco; said sensing means regulating the proportion of moisturized air that is heated prior to its contact with the tobacco at the tobacco introduction station.

2. The invention in accordance with claim 1 wherein means are provided for cooling the tobacco following removal from the air in the system.

3. The invention in accordance with claim 1 wherein means are provided for removing from the air water droplets and tobacco dust.

4. The invention in accordance with claim 1 wherein means are provided for regulating the temperature of the air independently-of regulation of its water vapor content.

5. The invention in accordance with claim 1 wherein chamber means containing bafile plates is provided in the system and located at a point prior to the air heating station for cooperating in decreasing the water vapor content of the air by having the moisture in the air impinge and collect on the baffle plates for eventual removal therefrom.

6. The invention in accordance with claim 1 wherein the system includes duct-work and the chamber means includes at least one chamber of somewhat enlarged proportions through which the tobacco is conveyed upwardly by the air and in which the velocity of said air is substantially lower compared to that in the reduced duct-work.

7. The invention in accordance with claim 1 wherein the heating means includes a by-pass through which a certain portion of the air is not heated depending upon the temperature of the air subsequent to the discharge of the tobacco from the system.

8. The invention in accordance with claim 1 wherein regulating means is provided for regulating the in-flow of fresh air into the system to maintain a substantially constant air temperature prior to the location at which the air is heated.

9. The invention in accordance with claim 1 wherein the air to tobacco ratio is at a value between'0.5 to 5 c.f.m. per pound of tobacco per hour.

10. The invention in accordance with claim 1 wherein the temperature of the air stream immediately prior to the introduction of the tobacco into the system is at a value between 150 to 600 F.

11, The invention in accordance with claim 1 wherein the temperature of the tobacco introduced into the .system is at a value between ambient temperatures and 200 F.

12. The invention in accordance withclairn 1 wherein the temperature of the air at such time as the tobacco is discharged from the system is at a value between F. and 200 F.

13. The invention in accordance with claim 1 wherein the amount of air bled off is at a value between 5% and 100%.

14. The invention in accordance with claim 1 wherein the temperature of the air prior to the air being heated is at a value between and F.

15. The invention in accordance with claim 1 wherein the moisture content of the tobacco introduced into the system is at a value between 16% and 35%.

16. The invention in accordance with claim 1 wherein the moisture content of the tobacco introduced into the system is at .a value between 18% and 25%.

17. The invention in accordance with claim 1 wherein the moisture content of the tobacco discharged by the system is substantially uniform and at a value between 9% and 23%.

18. The invention in accordance with claim 1 wherein the moisture content of the tobacco discharged from the system is substantially uniform throughout and is at a References Cited UNITED STATES PATENTS 2,229,943 1/1941 Touton 131-140 3,010,576 10/1961 Harte et a1.

10 FOREIGN PATENTS 287,421 3/1928 Great Britain. 875,684 7/1961 Great Britain. 158,380 3/1957 Sweden.

SAMUEL KOREN, Primary Examiner.

MELVIN D. REIN, Examiner. 

1. APPARATUS FOR HUMIDIFYING AIR AND DRYING TOBACCO COMPRISING MEANS FOR CIRCULATING THE SAID AIR IN A SUBSTANTIALLY CLOSED SYSTEM, MEANS FOR HEATING THE AIR IN THE SYSTEM, MEANS FOR INTRODUCING TOBACCO AT ONE END OF THE SYSTEM AND IN THE PATH OF THE HEATED AIR, MEANS IN ADVANCE OF SAID TOBACCO INTRODUCTION STATION FOR MOISTURIZING THE AIR SO THAT THE AIR INITIALLY CONTACTING THE TOBACCO CONTAIN A PREDETERMINED AMOUNT OF MOISTURE, CHAMBER MEANS IN THE SYSTEM AT A POINT BEYOND THE TOBACCO INTRODUCTION STATION AND IN WHICH THE TOBACCO IS CONVEYED UPWARDLY BY THE HOT MOISTURIZED AIR, THE AIR FLOW IN THE CHAMBER MEANS BEING INSUFFICIENT TO OVERCOME THE FORCE OF GRAVITY ON DENSER PORTIONS OF THE TOBACCO SO THAT SUCH DENSER PORTIONS WILL LOSE THEIR INITIAL UPWARD VELOCITY BEFORE REACHING THE TOP OF THE CHAMBER AND WILL SINK BACKIN THE OUTER PART OF THE CHAMBER AND EXECUTE A CIRCULATORY MOTION IN THE CHAMBER UNTIL THE DENSITY OF SUCH PORTIONS HAS DECREASED TO THE DESIRED DEGREE, MEANS FOR SEPARATIONG THE TOBACCO FROM THE CONVEYING AIR, MEANS FOR DISCHARGING AN AMOUNT OF MOISTURE-LADENED AIR FROM THE SYSTEM, MEANS FOR INTRODUCING THE EQUIVALENT AMOUNT OF FRESH AIR AT A LOWER MOISTURE CONTENT INTO THE SYSTEM, AND TEMPERATURE-SENSING MEANS FOR SENSING THE TEMPERATURE THE AIR FOLLOWING THE DISCHARGE OF THE TOBACCO; SAID SENSING MEANS REGULATING THE PROPORTION OF MOISTURIZED AIR THAT IS HEATED PRIOR TO ITS CONTACT WITH THE TOBACCO AT THE TOBACCO INTRODUCTION STATION. 